Post-surgery pain control is one of the most difficult problems faced by healthcare professionals. At the present time, there are roughly two frequently-used analgesics: the anesthetic analgesics (opioids), and the non-steroidal anti-inflammatory drugs (NSAIDs).
The opioid-type of analgesics acts on the central nervous system and provides relief for moderate to severe pain. Though in the management of severe pains, opioids are very potent pain relievers, they have the history of developing tolerance, drug abuse, physical and mental dependency, withdrawal symptoms and adverse effects, which make their uses controversial.
Nonsteroidal anti-inflammatory drugs (“NSAIDs”), on the other hand, are widely used for treatment of minor discomfort and illness and many disease conditions such as cold, aches and pains, mild fever, osteoarthritis, rheumatoid arthritis, acute or severe pain, etc. At the present time, NSAIDs are among the most prescribed drugs in the world, with annual sales exceeding $6 billion.
NSAIDs are a family of drugs that generally have analgesic, antipyretic, and anti-inflammatory activities. These activities derive from a common mechanism: the inhibition of cyclooxygenase, which is the critical enzyme for biosynthesis of prostaglandins, prostacyclin, and thromboxanes. Because prostaglandins are released in response to inflammatory stimuli, which in turn result in inflammatory responses (e.g., redness, pain, heat and swelling of tissue), inhibition of prostaglandins by NSAIDs results in analgesia. In the central nervous system, NSAIDs are antihyperalgesic through a direct action on the spinal cord.
One NSAID, ketorolac, which belongs to the acetic acid class of NSAIDs, are comparable to opioids in terms of providing pain relief. Its salt form, ketorolac tromethamine is a highly potent non-narcotic analgesic with a moderate anti-inflammatory activity. It is efficacious in treating pain arising from a broad spectrum of causes, such as postoperative pain, cancer pain, migraine headache and pain from dental extractions. (Suayib et al. Acta Oncologica 36: 231-232, (1997); and DeAndrade & Maslanka, Orthopedics, 17: 157-166, (1994)).
Ketorolac has less adverse side effects than narcotic drugs, does not have the side effects associated with opioids, and has not been shown to have physiological addictive potential. This drug appears to be an excellent choice for treating moderate to acute pain.
Ketorolac is a derivative of pyrrolizine carboxylic acid and is structurally related to tolmetin and zomepirac. The most commonly used form of ketorolac is ketorolac tromethamine. The chemical name for ketorolac tromethamine is (±)-5-benzoyl-2,3-dihydro-1H-pyrrolizine-1-carboxylic acid 2-amino-2-(hydroxymethyl)-1,3-propanediol. Its chemical structure is as follows: 
Ketorolac tromethamine has a pKa of 3.5 and an n-octanol/water partition coefficient of 0.26. The molecular weight of ketorolac tromethamine is 376.41.
Although NSAIDs are highly effective, their use in oral administration has been associated with significant adverse effects, most notably those involving the gastrointestinal (GI) system.
There are two major ulcerogenic effects of NSAIDs: (1) topical irritant effects on the epithelium of the GI tract, and (2) suppression of GI prostaglandin synthesis. In recent years, there have been numerous attempts to design and develop new NSAIDs that reduce damage to the GI tract. These efforts, however, have largely been unsuccessful. For example, enteric coating or slow-release formulations designed to reduce the topical irritant properties of NSAIDs have been shown to be ineffective in terms of reducing the incidence of clinically significant side effects, including perforation and bleeding. (Wallace and Chin, Drugs of Today, 33:115-122 (1997)).
Others have suggested combining the use of NSAIDs with other drugs which have the effect of eliminating or resisting GI side effects caused by NSAIDs (the so-called “prophylactic therapy”). For example, misoprostol can be used to make up for the prostaglandin deficiency caused by NSAIDs. Drugs that suppress the secretion of stomach acid, such as H2-antagonists or proton pump inhibitors, can also be used.
In the invention to be presented in the following sections, novel oral pharmaceutical compositions containing NSAIDs, particularly ketorolac tromethamine, are described. These pharmaceutical compositions contain an inert core, a drug layer, a protecting layer, and an enteric coating layer. The protecting layer protects the drugs from light and humidity. The enteric coating layer protects patients from ulcerogenic effects.